:root {
    --background-color: #2c3e50;
    --show_color1: #03a9f4;
    --show_color2: #f441a5;
}

* {
    margin: 0;
    padding: 0;
}

body {
    width: 100vw;
    height: 100vh;
    background-color: var(--background-color);
    display: flex;
    justify-content: center;
    align-items: center;
}

.bt {
    font-size: 30px;
    color: #FFF;
    background: linear-gradient(90deg, var(--show_color1), var(--show_color2));
    padding: 24px 48px;
    border-radius: 60px;
    position: relative;
    overflow: hidden;
}

.bt span{
    position: absolute;
    background-color: #FFF;
    border-radius: 50%;
    transform: translate(-50%,-50%);
    animation: show 1s;
}

@keyframes show{
    0%{
        opacity: 0.5;
        width: 0;
        height: 0;
    }
    100%{
        opacity: 0;
        width: 300px;
        height: 300px;
    }
}